Heat exchanger



columnar stresses within the fins.

I Unlted States- Patent 1 1 3,542,124

[72] Inventors Joseph N. Mann-ado 5 R f n s cited UNITED STATES PATENTS m: $223,122 33:35: 2,997,280 8/1961 Keast 165/157X c'mom'h 3,016,921 1/1962 Tadewald 165/166X 2" A I No 751288 3,196,942 7/1965 Prentiss..... 165/166 E f A a 1968 3,262,496 7/1966 Bawabe..... 165/166 [45] Patemed s}; 1970 1,805,652 5/1931 Caracristi... 165/166 in 2,033,402 3/1936 Smith 165/166X [731 mg: 22?": n 3 079 994 3/1963 Kuehl 165/166 I n" on a I a comma creditor. 3,282,334 11/1966 Stahlheber 165/166 Primary Examiner-Robert A. O'Leary Assistant Examiner-Theophil W. Streule Attorney-John N. Hazelwood, Edward B. Johnson, Albert J. g 4 HEAT EXCHANGER Miller and Orville R. Seidner 1 Claim, 1 Drnwln'g Fig; [52] 11.8. (21..., .Q 165/166 ABSTRACT: In a heat exchanger having passageways formed llli-cl between spaced parallel plates bounded in a stack with fins [50] Field of Search connecting adjacent plates, means are provided for relieving Patented Nov. 24, 1970 r 3,542,124

INVENTORS. JOSEPH N. MANFREDO DAVID G- BRIDGNELL BY SOREN K. ANDERSEN ATTORN EY This invention-relates to a heat exchanger; constructed, in

particular, of a plurality of plates'disposed in a stack and spaced from each other'with fins bonded to two adjacent plates. a v

Within heat exchangers of the type above described, one fluid flows between two adjacent plates to give up heat to another fluid that flows on the opposite side ofthe'respective plates. Finsare' provided between the plates to more readily extract the heat from one fluid and transfer it to the other. To minimize friction, the fins aredisposed parallel to the fluid flow, providing a path for heat flow without adding appreciable flow resistance. In addition, the thickness of the fins is such as to. provide maximum flow area, maximum wetted surface, and maximum area for heat flow. A relatively thin fin normally satisfies thisr'equirement. However, a thin fin buckles or bends under relatively light compression loads such as may be encountered at the inlet end for the hot fluid. The fins are subjected to repeated buckling whenever the system is started and stopped due to the thermal cycle formed by theheating and then cooling of the heat exchanger. Then, after a few thermal cycles, the fins become stress fatigued and break. When this happens to the fins within the high pressure passageways, the

platesare subjected to repeated bending by the'higher pressure fluid whereby the plates become fatigued and break,

causing an intermixing of the coolant and fluid to be cooled.

Therefore, an object of this invention is to provide added columnar support to the fins without decreasing the area of fluid flow.

Another object of this invention is to provide an improved lightweight heat exchanger.

These and other objects, features and advantages will become more apparent from the following description of the invention and shown in the accompanying drawing wherein the sole figure schematically shows an enlarged pictorial view of the heat exchanger incorporating the invention.

Referring to'the drawing, the heat exchanger has a plurality of spaced parallel plates 11 having preferably a' rectangular shape. Between alternate spaces formed by the plates lland along opposite edges thereof are bonded edge" closure elements 1 2a and12b. T he edge closure elements 120 and 12b along one of the respective edges are shown, the opposite plate edges, not shown, have, similar edge closure elements bonded thereto to form a plurality of passageways 13a and 13b which are parallel to each other. Passageways Home located outside of passageways 13b and edge closure elements 12a are, for example, one-half as wide as edge closure elements 12b, making passagewaysflSa narrower than passageway 13b. This arrangement is preferredsince, as it will become apparent, the fluid in the outer passageways 13a can only absorb or give up heat on one side thereof instead of two sides like the fluid within passageways 13b. The remaining spaces between the plates have edge closure elements 16 bonded to the two other opposing edges of the plates 11. Only the edge closure elements 16 along one of the other edges are shown, but

similar edge closure elements are understood to be bonded to the opposite edgesto form parallel passageways 17. One end passageways 17 through the ends thereof shown in the drawir" words, all the plates'and fins experience thermal expansion but are restrained by the corner edges. This restraint imposes compression loading on the fins. When the temperature gradientis too large, the fins in some of the passageways have been observed tobend and buckle. The fins 23 fatigue when the fins are repeatedly buckled under this compression loadingdue to the cycle of thermal expansion and contraction. When the fins in a high pressure passageway crack or break, the plates 11 bend due to the pressure differential thereacross. Themafter more cycling of the heat exchanger, plates 11 fatigue and break causing the hot and cold fluids to intermix.

One method of preventing the fins from breaking is to increase the number of fins per inch; but obviously, theflow area for the fluid decreases in about the same relationship as the increase in the number of fins'and, in turn, the flow area decreases almost directly with increases-in buckling strength. Another method is to make the fins thicker. Since the compression strength increases as the cube of the thickness and since the flow area decreases as fin thickness increases, the flow area decreases approximately as the cube root of' the buckling strength increases. in other words, an increase by a factor of two in the fin buckling strength decreases the flow area by approximately one-quarter. This invention teaches another method which is unique and novel, i.e., the use of relatively thick bars in combination with the fins so that the flow area remains substantially constant as the buckling strength is increased. Then where the temperature gradient is less severe, the bars are discontinued and fins only are provided for efficient heat conduction between the fluids.

The fins in this embodiment have different configuration within the various passageways; Passageways' 13a have fins 21,

.be'encount'ered. For. clarity in the drawing, the relative 26 do not extend the full length of the passageway since the of each of the passageways 13a and 13b communicates with an inlet manifold (notshown) and the other end communicates with an outletmanifold (not shown). In addition, opposite ends of passageways l7 communicate respectively with inlet and outlet manifolds (not shown), in a manner well known in the art.

The plates 11 should be of minimum weight and are made as then as possible. l-lowever,'the fluid passing within one group of parallel passageways may be at a higher pressure than the fluid passing within the other group of parallel passageways. This pressure differential tends to bend the thin plates. As mentioned above, suitable fins are normally bonded to adjacent plates 11 and these fins are capable of safely withstanding' tensile stresses due to any pressure differential. Therefore, the fins help to maintain the plates 11 flat. However, the two fluids, in addition to having unequal pressures, have inherently unequal temperatures. Therefore, if the hot fluid enters the modate the width' of the respective passageways. The passageways 17 have fins 23 at the inlet side thereof and extend a predetermined distance into the passageway. Fins 23 are followed by fins-24 which preferably give more corrugations per unit length than fins 23. The fins 23 are disposed at the inlet end of the higher pressure fluid, where the tempera- 'ture gradient isgreater so that means, in the form of the aforementioned bars 26, are placed longitudinally within passageways 17 to withstand any compressive force that may thickness, of the various plate elements are not shown to scale.

The bar thickness is chosento provide maximum strength and minimum loss to flow area within the passageways. The, bars temperature gradient is less severe as the fluid passes through the heat exchanger. The fins 23 preferably extend along the passageway the same distance as the-bars 26. With this arrangement the flow area through the passageways 17 can be made substantially optimum and uniform. Means, such as bars 26, are placed withinjpassageways 13a and I'Sbbut normally, since the pressure therein is lower than the other passageways, the heat exchanger will not fail if the fins 22 happen to break. Various other modifications may be contemplated by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the following claim. We claim:

l. A heat exchanger comprising: a plurality of spaced parallel plates; a plurality of first edge closure elements arranged between alternately spaced parallel plates to define a plurality of 7 first passageways for receiving a first fluid;

a plurality of second edge closure elements arranged between the alternately spaced parallel plates not includa plurality of first corrugated fins disposed between adjacent parallel plates at the inlet ends of the first and second passageways, said first corrugated fins offset to provide lateral support alternately to the long sides of said bars; and

a plurality of second corrugated fms disposed throughout the remainder of said first and second passageways, said second offset corrugated fins having more corrugations per unit length than said first offset corrugated fins to provide substantially the same flow area as the flow area at the inlet ends of the first and second passageways having said first corrugated fins and said bars. 

